1. Field of the Invention
The invention relates to a bottom anode for a metallurgical vessel destined for producing a metal melt, preferably a steel melt, which bottom anode is formed by a metal bar, preferably a steel bar, provided with at least one through recess extending from outside of the metallurgical vessel as far as to within the metallurgical vessel, as well as to a process for producing a bottom anode and a process for operating a metallurgical vessel equipped with a bottom anode according to the invention.
2. Description of the Related Art
In order to maintain a direct current flow inducing an electric arc, one or several bottom anodes are arranged on the bottom of a metallurgical vessel, such as a direct current electric arc furnace, and are connected with the rectifier unit in a conductive manner.
Several types of bottom anodes have been known, their service lives, as a rule, ranging between some hundred to a maximum of about 1,500 melts. Thus, this service life lies considerably below the service life of the lining of a metallurgical vessel, which is made of refractory material. As a result, known bottom anodes must be replaced several times during the service life of the lining of a metallurgical vessel, which constitutes problems in respect of the procedure as such, the operational interruption involved and the connection of the bottom anode with the refractory lining of the metallurgical vessel. A widespread type of bottom electrode is the water-cooled billet or bloom anode, which is known, for instance, from DE-A-38 35 785 and from EP-A-0 133 925. In that case, one or several, suitably water-cooled, steel billet(s) or bloom(s) is/are inserted in the refractory lining of a brickwork of the metallurgical vessel and serve to transmit current to the melting stock. In the lower part of the billet or bloom anode, a copper bar is attached to the upper steel bar, which copper bar is intensively cooled with water and carries off heat, thus safeguarding a certain period of operation of the steel bar for the transmission of current to the melting stock.
However, during operation the refractory material around the anode bar is being washed out by the steel melt, the steel bar, thus, being worn, too. If such wear has reached a certain extent, the bottom anode must be replaced. This involves the drawbacks described above.
From EP-A-0 527 363, a bottom anode for an electric arc furnace of the initially defined kind is known, with which an electrode is integrated in a refractory ceramic body, thus forming a type of a flushing electrode. Thereby, the supply of flush gas, such as oxygen or inert gas, is to be ensured. In fact, such a flushing electrode is comprised of a central bar-shaped electrode that is surrounded by a steel tube concentrically and in a spaced-apart manner, the steel tube being enclosed by a refractory ceramic body. The flush gases are introducible through the annular gap provided between the steel tube and the electrode. According to another embodiment, the electrode itself incorporates gas channels for feeding a treatment gas. It is true that some kind of cooling effect of the bottom anode may be achieved by the flush gas injected, yet no decisive increase in its service life will be obtained thereby.